Re: [PATCH 3/3] riscv: keep booting if KFENCE pool reservation fails

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] riscv: build failure on 32-bit and NOMMU from including asm/kfence.h
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commit d964a4c4107a3db6e2c99928c0888060598196ba
Author: Jackie Liu <liuyun01@kylinos.cn>

riscv: keep booting if KFENCE pool reservation fails

This commit avoids hitting BUG_ON() when the early KFENCE pool reservation
fails in create_linear_mapping_page_table(), disabling KFENCE instead so the
kernel can continue booting.

> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index fb37b0b67efec..393106cd25ba0 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -27,6 +27,7 @@
>  #include <asm/fixmap.h>
>  #include <asm/io.h>
>  #include <asm/kasan.h>
> +#include <asm/kfence.h>

[Severity: Low]
Does including asm/kfence.h unconditionally in arch/riscv/mm/init.c break
32-bit (CONFIG_32BIT=y) and NOMMU (CONFIG_MMU=n) RISC-V builds?

arch/riscv/mm/init.c is built unconditionally for all RISC-V configurations,
whereas HAVE_ARCH_KFENCE is only selected when MMU && 64BIT. In
arch/riscv/include/asm/kfence.h, kfence_protect_page() is defined outside of
any CONFIG_KFENCE guard:

arch/riscv/include/asm/kfence.h:
static inline bool kfence_protect_page(unsigned long addr, bool protect)
{
	pte_t *pte = virt_to_kpte(addr);

	if (protect) {
		set_pte(pte, __pte(pte_val(ptep_get(pte)) & ~_PAGE_PRESENT));
	} else {
		set_pte(pte, __pte(pte_val(ptep_get(pte)) | _PAGE_PRESENT));
		mark_new_valid_map();
	}

	preempt_disable();
	local_flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
	preempt_enable();

	return true;
}

On 32-bit builds, mark_new_valid_map() is not declared because
arch/riscv/include/asm/cacheflush.h guards it under
#if defined(CONFIG_64BIT) && defined(CONFIG_MMU) with no fallback stub.

On NOMMU builds, virt_to_kpte() in include/linux/pgtable.h,
set_pte() / __pte() / pte_val() / ptep_get() in
arch/riscv/include/asm/pgtable.h, mark_new_valid_map() in
arch/riscv/include/asm/cacheflush.h, and local_flush_tlb_kernel_range() in
arch/riscv/include/asm/tlbflush.h are all guarded by #ifdef CONFIG_MMU and
are undeclared when compiling kfence_protect_page().

Should the include in arch/riscv/mm/init.c or the contents of
arch/riscv/include/asm/kfence.h be guarded by #ifdef CONFIG_KFENCE?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1793017073.git.liuyun01@kylinos.cn?part=3